knife tool not ending
If you selected the knife tool in the sidebar on the left, you can just select a new tool (Select Box, the top one, is the default):



Here, the knife tool is selected, so any time you click, it will use the knife. Just select the first box, and it will go back to the default.

Personally, I just use the knife tool by pressing k, and then after i press space to end the cutting, it will automatically go back to normal mode.